Amongst the very many types of arch-work and girder-work adopted for railway purposes, the following examples from actual practice may be useful for reference:-- [Illustration: Fig. 126, 127] Fig. 126 represents small 24-foot span, low viaduct arching suitable for a line passing through towns or villages, where ground is valuable and the area to be covered must be kept as small as possible. The arches may be utilized for stables, stores, or roads of communication between the lands and properties intersected by the railway. The segmental form gives a better headway underneath than the semicircular, besides containing less material in the arching proper, and requiring a smaller amount of centering. Every precaution should 131 be taken to prevent water percolating through any portion of the arching, or haunching, and a thick layer of good asphalte should be placed over the entire upper surface, and carried well up the lower portion of the parapet walls, as shown on the sketch. The cast-iron pipes with rose heads form a very efficient means of taking away the rain-water which filters through the ballast and filling. The pipes should be carried down in chases, or recesses, built in the fronts of the piers, to protect them as much as possible from injury in the yards below. Rose heads, pierced with holes, and surrounded with small stones hand-laid, serve well to conduct the water into the pipes. Where the arching is of considerable length, recesses or refuges for the platelayers may be obtained by substituting a short length of cast-iron-plate parapet, instead of the stone or brick parapet, over some of the piers, as indicated in the sketch. Fig. 127 shows a similar description of arching for spans of 30 feet. The above two examples represent plain substantial work, but if circumstances warrant more external finish, this can readily be added without interfering with the general arrangement. In a similar manner, if considered preferable, the arches may be made semicircular or elliptical. In the sketches shown of the arched over-line and under-line bridges, the arching and coping of parapets are in brick, and the remainder of the work in stone. In very many cases brick will be found cheaper and more expeditious for arching than stone, unless the quarries turn out stone in blocks which can be conveniently trimmed for arching. All bricks used for arch-work should be hard and well burnt, and special care should be taken in the selection of those to form the under-side course, which will be exposed to the atmosphere. For moderate spans arches have been successfully constructed of concrete. For this description of work the materials should be carefully gauged and mixed together, and the finished work should be allowed to stand some time on the centres to allow the concrete to become thoroughly set. [Illustration: Fig. 131]